Environmental government dependences demand fuels with low content of metals such as sulphur, nitrogen, nickel vanadium, among others. Moreover, in order to take advantage of oil reserves, it is necessary to process each time heavier oils, than, the content of such contaminants increase in produced fuels, thus, it is necessary to develop new processes and catalytic materials for the elimination of this contaminant from hydrocarbons or fossil fuels in a most efficient way, to minimize polluting gas exhausts to the atmosphere, to satisfy the ecologic regulations that are turning more strict with the time. The most efficient industrial processes for polluting removal from fossil fuels are the hydroprocessing processes, which are practically applied to all petroleum fractions, such as fuels, diesel, intermediate and heavy distillates, heavy strait run gas oil (Feeding to Fluid Catalytic Cracking, FCC). For the specific case of the present invention light and intermediate petroleum fractions are considered, those comprising hydrocarbons whose boiling points are equal or lower than 180° C. and intermediate petroleum fractions, those comprising hydrocarbons whose boiling points are equal or higher than 180.1° C. and lower or equal to 400° C.
In the hydroprocessing processes the light and intermediate petroleum fractions are hydrotreated and/or hydrodesintegrated in the presence of hydrogen. The hydroprocessing processes comprise all processes in which a hydrocarbons fraction reacts with hydrogen at high temperature and pressure, and include processes such as: hydrogenation, hydrodesulphurization, hydrodenitrogenation, hydrodemetalization, hydrodearomatizacion, hydroisomerization, hydrodesintegration.
The catalysts used in hydroprocessing processes are mainly constituted of at least one metal from group VIII and at least one non noble metal component from group VIB from the periodical table, deposited in a specific high area support constituted by metal oxides, such as alumina, silica, titania and/or mixtures, containing optionally a secondary promoters or additives such as halogen, phosphorous, boro, etc. Catalysts are generally prepared by impregnating supports with aqueous solutions containing metals compounds, followed by drying and calcination procedures. Preparation procedures for hydroprocessing catalysts have been stated in U.S. Pat. Nos. 5,089,462 and 2,853,257 as well as in European patents EP 0,448,117 and 0,469,675.
Commonly used supports are based on a refractory material constituted of alumina. The molybdenum-alumina catalysts promoted with cobalt are generally used when limiting specifications are only hydrodesulphurization, while molybdenum-alumina catalysts promoted with nickel are widely used when hydrodenitrogenation and partial saturation of aromatic (hydrodearomatization) content is required besides hydrodesulfurization, due to the high hydrogenating activity inherent to nickel.
On the other hand, it has been determined that incorporating metal components from IVB group from the periodical table, such as titanium, in hydrotreating catalysts as promoters, increase the catalytic activity (U.S. Pat. Nos. 5,089,462, 4,388,222). Also incorporation of other components like phosphorous, boron, etc., to the hydroprocessing catalysts promotes the catalytic activity by an increase in the support acidity (U.S. Pat. No. 3,840,473). However, the phosphorous content cannot be higher than 0.5 wt. % in catalyst containing titanium as promoter, because it contributes to the decreasing of the catalytic activity.
The desulphurization activity of molybdenum increases from two to four times, when the refractory material used as supports consists of titanium oxide. However, nanocrystalline titanium oxide presents low surface area, around 50 m2/g, being the reason of a non yet successful commercial application (Japanese patent JP 55125196). To increase the specific activity in titanium oxide based catalysts, the manufacturers have resorted to mixtures of titanium oxide with other oxides such as: titanium-alumina, titanium-zirconium, titanium-hafnium, etc., as supports for hydrotreating catalysts, obtaining specific area between 150 to 200 m2/g, depending on the method used for its synthesis. However, increases achieves in the hydrodesulphurization activity in such catalysts have been very small compared to the alumina based catalysts; which has not been substituted due to its low cost.
Recently, Inoue et al. (Prepr. Pap.-Am. Chem. Soc. Div. Fuel Chem, 2003, 48 (2), 497) have reported the synthesis of titanium oxide based supports with high specific area through a pH swing method, which consists of precipitating and dissolving the smallest polymeric particles of titanium oxyhydroxide formed during precipitation. The addition of an acid solution, dissolve the smallest particles, which are precipitated with the addition of a base solution. With this synthesis method, homogeneous nanoparticles of titanium oxide with anatase structure are obtained. The crystallite sizes are between 7 and 10 nm, they are thermally stable at temperatures as high as 500° C. and they present surface areas between 150 to 200 m2/g. By incorporating molybdenum and cobalt as active phases to this TiO2 support, the activity to hydrodesulphurization and hydrodenitrogenation reactions increase two or three times more compared with alumina based catalysts. The authors report low hydrogen consumption with molybdenum cobalt on TiO2 catalysts compared with alumina based catalyst, which increase potential application.
The most relevant advances recently achieved concerning hydroprocessing catalysts for hydrodesulfurization and hydrodesnitrogenation reactions are those based on nickel molybdenum-tungsten non supported phases (U.S. Pat. No. 6,534,437, 6,582,590). These Ni—Mo—W—S bulk catalysts present high specific areas between 150 to 200 m2/g. Hydrodesulphurization activity of such catalysts was measured with a Dibenzothiophene molecule. They present a specific activity measured in [molecules/g*s], similar to the conventional catalysts supported on alumina. However, these kind of catalysts present high density, then, in a volume unit high amount of catalysts is loaded than with a conventional catalyst, then the volume relative activity is around four times higher compared to the conventional nickel-molybdenum supported on alumina catalysts commercially available. These catalysts are only constituted of active phases and the cost associated to its production is high.
The discovery of the C60 carbon fullerene structure in the 80s, which consists of a hollow sphere with walls made up of sixty carbon atoms (H. W. Kroto, et al. Nature, 318, 162-163, 1985), gave rise to a new kind of materials, called carbon nanotubes (Iijima, S. Nature, 354, 56-58, 1991). By increasing the amount of carbon atoms in the fullerene structure give rise these ellipsoidal forms, named nanotubes. These nanotubes present semiconducting properties interesting for the construction of nanoelectronic devices. On the other hand, manufacturing of nanotubes has been extended to inorganic materials, and in 1992, the first inorganic nanotube with fullerene structure were obtained constituted of MoS2 and WS2 (R. Tenne et al. Nature, 360,444-446, 1992). Nanotubular morphology has extended toward other materials constituted by inorganic oxides, such as VO2, ZrO2, TiO2, Sio2, Al2, Al2O3, ZnO, TeO2, etc., and others kind of inorganic materials like sulphurs, selenides, telures, nitrides and carbides of transition metals (C. N. R. Rao and M. Nath, Dalton Trans. 1-24, 2003).
A series of studies on confined fluids, M. Lozada y Cassou et al. (J. Chem. Phys. 80, 3344-3349 (1984); J. Chem. Phys. 92, 1194-1210 (1990); J. Chem. Phys. 98, 1436-1450, (1993); Mol. Phys. 86. 759-764 (1995); Phys. Rev. E. 53, 522-539 (1996), Phys. Rev. Letts. 77, 4019-4022, (1996); Phys. Rev. E. 56, 2958-2965, (1997), phys. Rev. Letts. 79, 3656-3659 (1997)), showed that a nano-scale confinement and curvature, produce electric fields and molecular strengths of outstanding intensity. These studies show, for example, that in nano-confinement a charge separation in a ionic fluid can be produced (Phys. Rev. Letts. 79, 3656-3659 (1997)) implying confinement pressures in the order of 25 atmospheres and intermolecular repulsion strengths of 3.7×109 Newtons. These results led towards the search or tubular structures, at nanometric scale, for new materials with catalytic or semiconducting properties.
The nanotubes are strategic materials for applications where adsorption phenomena is involved, as they increase the contact area while exposing the inner and outer surfaces, the vertices and the surface of the interlaminar regions of the nanotubes walls. Besides the increase of the strength fields intensity due to nanotube confinement and curvature, must to improve catalytic activity in materials using nanotubes as supports of active phases. Therefore, we decided to look for new routes for the synthesis of inorganic oxide nanotubes, which would increase the specific surface area displayed by materials and provide a large contact area and confinement surface to perform catalytic processes.
The appliers have recently presented a PCT MX 03/00068 patent application, dated Aug. 22, 2003, regarding a procedure for the synthesis and thermal stability of nanotubes and or hydrogen titanate and titanium oxide nanofiber with orthorhombic structure. These one-dimensional nanostructures present high specific surface areas between 100 and 500 m2/g, and they are thermally stable at temperatures above 400° C., that is why they can be used as active phases supports of the metal component from group VIII and non noble metal components from group VIB for the formulation of hydroprocessing catalysts, being one of the reason of the present invention.